The present invention relates to an anti-locking control system for four wheeled vehicles in which the brake pressure at two of the four wheels is regulated jointly through the use of a brake pressure regulating unit and in which signals providing information about the rotational movement behavior of two diagonally oppositely disposed wheels of the vehicle are fed to an evaluation circuit which produces therefrom brake pressure control signals for the pressure regulating unit.
Such an anti-locking control system is known from the periodical "Auto-Motor-Sport", Issue No. 26,1973, pages 20 and 22. Based on the fact that the acceptance of anti-locking control units is hampered by their price, this article primarily describes an anti-locking control system in which the regulation is effected only by the pressure at the rear wheels and this with the aid of two sensors associated with these wheels as well as with a select-low type of control. When too much pressure is applied, this system results in blocked and thus uncontrollable front wheels on the vehicle.
The publication further mentions that instead of regulating the two rear wheels, it is possible to regulate only the wheels of one diagonal of the vehicle if a negative steering caster is provided. In this case, when the front axle is braked too heavily, the front wheel included in the regulating system will master the regulating action. Thus, in this case, the wheels of the unregulated diagonal will block when too much pressure is applied, the front wheel included in the regulating system is under control and thus steering capability is maintained and the second rear wheel will generally contribute little to the braking action. This system produces stability problems particularly on slippery, wet roads since the regulated diagonal is almost without pressure due to the low braking action of the front wheel so that a great difference in braking pressure results at the rear axle. Furthermore, on wet roads a great difference in braking pressure will occur at the front axle when the unregulated wheel locks.